1. Field of the Invention
This invention relates generally to the welding of two ends of steel pipe together, and particularly to welding of pipe ends together where the pipe is lined with fiberglass.
2. Description of Prior Art
Corrosion in oil and gas pipelines and flow lines continues to be a problem. The most common prevention technique for internal corrosion in the oil and gas industry at this time is coating the inside of the pipe with commercially available plastic or cement. Plastic or cement linings for pipe have proven to be not durable enough during xe2x80x9cpiggingxe2x80x9d operations to prevent damage of the lining and subsequent corrosion of the pipe.
A proven method of preventing corrosion in down hole applications is to line the pipe with glass reinforced epoxy (GRE), or fiberglass liners. Segments of down hole pipe are coupled together with threaded connections. Nevertheless, pipe segments lined with fiberglass for pipeline use must be welded end to end to form the pipeline. Specialized welding techniques have been required to weld fiberglass lined segments together.
Conventional welding techniques commonly used in the pipeline industry damage the fiberglass liners of the pipe. The heat generated by the weld greatly exceeds the working temperature of the liners.
Another concern of welding two pipe end segments together concerns alignment of the two pipes being welded.
A prior method used for welding fiberglass lined pipes without damaging the liners employs a sleeve manufactured by RICE ENGINEERING CORPORATION. The sleeve, called a DUOWELD sleeve, is welded to the pipe""s outside diameter prior to the lining operation. A special coupling with a corrosion barrier ring is also provided. DUOWELD sleeves allow an air gap between the outer weld of the sleeves and the coupling. The coupling includes a corrosion barrier ring to provide a continuous corrosion resistant surface on the inside of the lined pipe and coupling.
This prior RICE ENGINEERING method requires pre-welded sleeves and a coupling welded in the field. The two pipes must be xe2x80x9cjackedxe2x80x9d together to allow a significant amount of compression on the corrosion barrier ring. The DUOWELD product requires a total of four welds on each assembly. Two welds are performed on the sleeves, on each end of the pipe prior to the lining operation. Two additional welds are required to join the sleeves and the coupling after the jacking operation. Although the RICE ENGINEERING method has certain advantages, it has disadvantages of excessive cost due to the additional weld sleeve requirements, and the xe2x80x9cjackingxe2x80x9d operation.
Another prior method for end-to-end welding of fiberglass lined pipe is provided by CCB INTERNATIONAL. The CCB method utilizes an internal sleeve or fitting that fits inside of the pipe. The sleeve has an insulation material fitted over a PTFE (glass reinforced Teflon), or corrosion resistant alloy (CRA) tube. The inner tube has seal rings which engage the inside diameter of the liner. The sleeve significantly reduces the inside diameter of the joined pipe segments in the connector/weld area. Reduction of inside diameter at the connection is disadvantageous, because flow through the pipe is significantly restricted in the pipe joint area. Special procedures for tools such as pipeline inside diameter inspection tools, or other tools referred to as pipe line xe2x80x9cpigs,xe2x80x9d are also required. There are concerns about the weld quality, because there are two different materials potentially in contact with the weld.
A common concern during welding operations is the alignment of the two pipes being welded together.
3. Identification of Objects of the Invention
A primary object of the invention is to provide a method and apparatus to weld fiberglass lined pipe segments end-to-end in the field using normal welding procedures.
Another object of the invention is to provide a method and a device for welding fiberglass lined pipe segments end-to-end where only one weld is necessary as compared to the multiple welding steps required when using the DUOWELD sleeve.
Another object of the invention is to provide a method and a device for welding fiberglass lined pipe segments end-to-end where ordinary welding procedures are used as compared to special welding procedures as required in the CCB method.
Another object of the invention is to provide a weld shielding device that protects the fiberglass lining when fiberglass lined pipe segments are welded end-to-end, where the device acts as a centralizer for aligning the two pipe segments together.
Another object of the invention is to provide a weld shielding device that provides a substantially smooth inside diameter of fiberglass lined pipe where the inside diameter has no weld beads or weld splatter common in normal welding operations.
Another object of the invention is to provide a weld shielding device and method for welding fiberglass lined pipe segments end-to-end to provide a substantially smooth transition of the inside diameter across the joining area of the pipe segments so that pigging operation problems of the joined pipe segments are reduced as compared to pigging operations through fiberglass lined pipe segments joined by prior methods and devices.
Another object of the invention is to provide a weld shield device which functions as a spacer for the weld, thereby eliminating the need for tack welding prior to a root weld pass.
Another object of the invention is to provide a device which shields the fiberglass linings of opposed end-to-end segments of fiberglass lined pipes from the high temperature of the weld.
Another object of the invention is to provide a weld shield device to reduce the cost of joining fiberglass lined pipe end-to-end as compared to the CRA tube of CCB INTERNATIONAL.
The objects identified above as well as other features and advantages are incorporated in a weld shield device that facilitates the welded connection of two pipe segments having fiberglass liners. The weld shield device includes commercially available insulation material applied about the outer surface of a sleeve body. The sleeve body is arranged and designed in coordination with the end profiles of the pipes to be joined to help establish a welding gap between the two pipe segments, and the insulation material reduces the transfer of heat from the welding operations to the fiberglass liners. The weld shield device has end profiles that allow it to couple with the ends of the pipe segments. In this coupling, the weld shield device at least partially occupies a cutout portion of the fiberglass liner.
In a first embodiment of the invention, a long neck of the weld shield device fits in a cutout portion between a fiberglass lining and the pipe segment. A short neck of the weld shield device fits radially inwardly of the end of the fiberglass lining to protect and provide a substantially smooth transition across the joining area. The end of the fiberglass lining of a pipe segment fits within a groove defined by the two necks.
In a second embodiment of the invention, the weld shield device couples with an adhesive material surface and a fiberglass-lining surface. A short neck of the weld shield device fits radially inwardly of the end of the fiberglass lining to protect and provide a substantially smooth transition across the joining area.